Cryogenic cable

ABSTRACT

A cryogenic cable enabling the transfer of considerable electric power, characterized in that the electrical insulating means, between two coverings capable of being brought to different electric potentials, consists essentially of a volume of gas at a pressure between 10 5 and 10 2 Torr.

United States Patent 174/16, 27,126 R, 126 CP,128; 335/216 THERMAL STEEL SCREEN Bobo et a1. 1 1 May 29, 1973 [54] CRYOGENIC CABLE [56] References Cited [75] Inventors: Jean-Claude Bobo, Saint-Michel- UNITED STATES PATENTS iz g i E 229 Om): 3,501,581 3 1970 Edwards ..174 15 c 3"2- "PP' lance 3,595,932 7 1971 Kafka ..174/15 c 9 3,512,581 5/1970 Lawton ..l74/15CX [73] Asslgnee' g 'l g Generale DElecmc'te 3,515,793 6/1970 Aupoix et a1 .,174 15cx 3,562,401 2 1971 Long.... ..174 15 c [22] Filed: Apt 14 1972 3,591,705 7/1971 Grigsby.... ..l74/15 C 3,612,742 10/1971 Snowden ..l74/15 C [21] App1.No.: 244,166

Primary Examiner--Bernard A. Gilheany Assistant Examiner-A. T. Grimley [30] Foreign Appllcatlon Priority Data Atwmey, Richard C sughrue et aL Apr. 14, 1971 France ..71 13090 3 [57] ABSTRACT [52] "174/15 174/126 174/128 A cryogenic cable enabling the transfer of considera- 174/DIG 6 ble electric power, characterized in that the electrical 51 Int. Cl. ..H01v 11/00, HOlb 7/34 insulating means between two coverings capable of [58] Field of Search ..174\/15 C, DIG. 6, being brought to different electric potentials consists essentially of a volume of gas at a pressure between 10' and 10 Torr.

5 Claims, 3 Drawing Figures INSULATOR Pmmzn w 3.736.365

SHEET 1 OF 3 FIG/1 SUPERCDNDUCTIVE COVERING THERMAL STEEL SCREEN ALUMINA INSULATOR COVERING PATENTEDRAYZQQY? 3,736,365

SHEET 2 OF 3 THERMAL STEEL SCREEN ALUMINA INS ULATOR COVERING PATENTE was 1975 SHEET 3 OF 3 INTERMEDIATE COVERING ALUMINA.

M L RE E T S INSULATOR N E E R c s STEEL COVERING 1 CRYOGENIC CABLE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the field of electric cryogenic cables.

2. Description of the Prior Art Very diagrammatically, an electric cryogenic cable of the known type comprises:

An internal metal covering or sleeve which is fluidtight, is suitable for conveying a cryogenic fluid and contains at least one electric conductor;

An external metal covering or sleeve which is fluidtight, and which is intended to be brought to an electric potential distinct from that of the internal covering; and

Electrical insulating means inserted between the internal covering and the external covering.

In such a cryogenic cable, the electrical insulation is essentially provided by insulating tape arranged between the internal covering and the external covering.

SUMMARY OF THE INVENTION The object of the present invention is to provide an electric cryogenic cable having electrical insulating means more effective than the insulating means referred to above.

A more specific object of the present invention is to provide an electric cryogenic cable comprising:

At least one internal covering or sleeve containing at least one electric conductor;

An external covering or sleeve which is fluid-tight which is outside the internal covering and which is intended to be brought to an electric potential distinct from that of the internal covering;

Means for cooling at least one of the coverings;

Means for thermally insulating the coverings from outside conditions;

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are diagrarnmatical sectional views of three embodiments of the invention. Analogous elements are given identical reference numerals in the three figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cryogenic cable shown in 'FIG. 1 comprises a metal internal covering or sleeve 1 which is fluid-tight and consists of an electric conductor 3, made of aluminum, for example, suitable for containing a flow of cryogenic fluid 2, such as helium.

The conductor 3 contains, within its ground conductor, several conductors 4, parallel to its generating lines, which may each consist of strands of superconductive material connected with stainless steel strands.

The conductor 3 may be enveloped in an insulating tape, made of ethylene-glycol polyterephthalate, for example, which is better known by its registered trade name, MYLAR.

The cryogenic cable comprises also an external covering 7, which is fluid-tight and is made of metal, such as steel, and which is arranged around the internal covering 1. A metallic thermal screen 8, which is not fluidtight when under vacuum, is preferably inserted between the two coverings 1 and 7; this screen is cooled by means of a cryogenic fluid 9, such as liquid nitrogen, flowing through the ducts formed in its walls.

A super thermal insulator, made of a powder containing mainly alumina, for example, occupies at least a part of the volume 10 formed between the thermal screen 8 and the external covering 7.

In such a cryogenic cable intended for carrying continuous current, the covering 7 is brought to the potential of the ground conductor and the covering 1 is brought to a very high voltage.

According to the invention, the space formed between the internal covering 1 and the external covering 7 is filled with gas, for example, helium, at a pressure between 10 and 10 Torr. It has been observed, indeed, that this gas under slight pressure made it possible to improve substantially the electric insulation of the cryogenic cable.

In the particular case shown in FIG. 1, the gas pressure is between 10 and 10 Torr, so as to remain compatible with the presence of the alumina powder.

The embodiment of a cryogenic cable shown in FIG. 2 is intended for carrying single phase alternating current.

An internal covering 20 comprises an inner support 25 made of resistant cryogenic material and cooled by means of a cryogenic fluid 27, such as liquid helium. The external face of the support 25 is provided with a superconductive layer 26.

Anexternal covering 30 comprises a support made of resistant cryogenic material 22, cooled by a cryogenic fluid 24, and provided on its internal face with a superconductive layer 23.

The covering 20 is intended to be brought to a high electric potential and the covering 30 to the potential of the ground conductor.

The space 28 separating the two superconductive layers 23 and 26 is filled with gas, such ashelium, at a pressure between 10' and 10 Torr, thereby enabling good electric insulation to be provided between these layers.

The cryogenic cable formed by the two coverings 20 and 30 is surrounded by a thermal screen 8, cooled by means of a cryogenic fluid 9, and by an external covering 7 which is fluid tight.

A thermal super-insulator preferably occupies the space 10 between the screen 8 and the covering 7.

The space between the coverings 7 and 30 is subjected to an extensive vacuum.

The various coverings are fixed to one another by appropriate insulating supports, not shown.

FIG. 3 shows an embodiment of a cryogenic cable intended for carrying three phase alternating current.

Such a cryogenic cable comprises three cables consisting respectively of three sets of conductors 40,41, 50,51, and 60,61, each being of a type analogous to the set 30,20 shown in FIG. 2.

The internal coverings 41, 51, 61, are intended to be brought to electric potentials having very high values, whereas the external coverings 40, 50, 60 are intended to be brought to the neutral potential.

The electrical insulation between two interconnected coverings is provided by volumes of helium 42, 52, 62 under a pressure between 10 and Torr. The coverings are cooled internally and externally by a cryogenic fluid 71 contained in a fluid-tight intermediate covering 70.

It must be understood that these three types of cryogenic cables have been given only by way of an example, it being possible to use the electric insulating means described above in all embodiments of such cables. 1

We claim: 1. A cryogenic cable comprising: a. at least one internal covering including at least one electric conductor; I b. a fluid-tight external covering, outside said internal covering and adapted to be brought to an electric potential distinct from that of said internal covermg; 0. means for cooling at least one of said coverings; d. means for thermally insulating said coverings from out-side conditions; and

e. means for electrically insulating said coverings from one another, said electric insulating means comprising a volume of gas at a pressure between 10 and 10 Torr and disposed between said coverings.

2. A cryogenic cable according to claim 1 wherein said internal covering comprises a resistant cryogenic support whose external surface is provided with a first superconductive layer, and wherein said external covering is coaxial with said internal covering and comprises a resistant cryogenic support whose internal surface is provided with a second superconductive layer, said first and second superconductive layers being electrically insulated form each other by said volume of gas.

3. A cryogenic cable according to claim 2, wherein said internal and external coverings form a set of coverings, and further comprising additional sets of coverings and an additional fluid-tight covering enclosing all of said sets of coverings and suitable for conveying a cryogenic fluid.

4. A cryogenic cable according to claim 1 wherein said gas is helium.

5. A cryogenic cable according to claim 2 wherein said gas is helium. 

2. A cryogenic cable according to claim 1 wherein said internal covering comprises a resistant cryogenic support whose external surface is provided with a first superconductive layer, and wherein said external covering is coaxial with said internal covering and comprises a resistant cryogenic support whose internal surface is provided with a second superconductive layer, said first and second superconductive layers being electrically insulated from each other by said volume of gas.
 3. A cryogenic cable according to claim 2, wherein said internal and external coverings form a set of coverings, and further comprising additional sets of coverings and an additional fluid-tight covering enclosing all of said sets of coverings and suitable for conveying a cryogenic fluid.
 4. A cryogenic cable according to claim 1 wherein said gas is helium.
 5. A cryogenic cable according to claim 2 wherein said gas is helium. 